1. Field of the Invention
The present invention relates to an advanced mobile communication, and more particularly, to a method for confirming a receipt of protocol data units (hereinafter, “PDU”) which can eliminate the starting point polling problem of the window-based polling algorithm used in a radio link control (hereinafter, “RLC”).
2. Background of the Related Art
Generally, “Polling” means that an originating system requests a receiving system to receive a status report. Then a radio link control (RLC) layer receives the status report from the receiving system and controls the error and/or data flow.
After the originating system sends a given set of radio link control protocol data units (RLC PDU) to the receiving system, the originating system sends a polling signal to the receiving system to check whether the receiving system has received all the data units properly. Then the receiving system sends the status report indicating an acknowledgement (hereinafter, “ACK”) or a negative acknowledgement (hereinafter, “NACK”) for each individual RLCPDU after checking a receiving status for all the data units which the originating system has sent.
A window based polling method is one of typical methods for transmitting a polling signal to the receiving system. When using the window based polling method, polling occurs if the number of RLC PDUs transmitted to the receiving system exceeds a predetermined limiting value. In other words, Polling occurs when the following condition is satisfied.                                           [                          1              -                                                                    (                                                                  Tx                        ⁢                                                                                                   ⁢                        _window                        ⁢                        _size                                            +                                              VT                        ⁢                                                  (                          MS                          )                                                                    -                                              VT                        ⁢                                                  (                          S                          )                                                                                      )                                    ⁢                  mod                  ⁢                                                                           ⁢                  Tx                  ⁢                                                                           ⁢                  _window                  ⁢                  _size                                                  Tx                  ⁢                                                                           ⁢                  _window                  ⁢                  _size                                                      ]                    ×          100                =                  X          >                      Poll_window            ⁢                          (              %              )                                                          [Equation  1]            
Tx_window_size in Equation 1 is a communication window size which represents the maximum number of RLC PDUs that can be transmitted at once in a communication system. VT(S) is a send state variable which represents the sequence number of the first PDU of the RLC PDUs subjected to be transmitted next, and it increases by one after each PDU is transmitted. VT(MS) is a maximum send status variable which represents the sequence number of the first PDU of the RLC PDUs not subjected to be transmitted. Therefore, the largest sequence number of the PDUs subjected to be transmitted is VT(MS)-1. The maximum send status variable forms an upper edge of the communication window, and its relationship to the communication window size is described in the following equation,VT(MS)=VT(A)+Tx _window_sizewhere VT(A) is an acknowledge state variable which represents the sequence number of the first PDU of the RLC PDUs required to receive an ACK signal for the next transmission, and it forms a lower edge of the communication window. Therefore, the value of VT(S) can be between VT(A) (minimum) and VT(MS)-1 (maximum).
After the originating system receives the status report indicating ACK/NACK status of each PDU sent to the receiving system, the value of VT(A) is updated to the sequence number of the PDU required to receive the next ACK, and VT(MS)is reevaluated by the above equation.
Poll_window in Equation 1 is a limiting value for the window-based polling algorithm which limits the number of the RLC PDUs subjected to be transmitted. In other words, the originating system sends the polling signal to the receiving system when the number of the transmitted RLC PDUs is larger than the predetermined value of Poll_window.
When VT(S) is equal to VT(A) in Equation 1, the value of X is 100 which is always larger than Poll_window. Therefore, the polling always occurs when transmitting the PDUs at the starting point of the communication window (VT(S)=VT(A)). This starting point polling problem reduces the data processing capacity of the whole communication system, and creates the protocol errors in the transmitting or receiving system.